Hydrocarbon conversion process



Aug. 20, 1957 F. E. FREY ETAL HYDROCARBON CONVERSION PROCESS Filed Jan. 25, 1952 I INVENTORJ F E FREY H.J. HEPP M M MW ATT NEYJ' United States Patent 2,803,684 HYDROCARBON CONVERSION PROCESS Frederick E. Frey and Harold J. Hepp, Bartlesville, Okla assignors to Phillips Petroleum Company, a corporation of Delaware Application January 25, 1952, Serial No. 268,162 Claims. (Cl. 260-673) This invention relates to the alkylation of hydrocarbons. In one of its aspects the invention relates to an improved process for the aromatization of hydrocarbons employing an improved pebble heater apparatus. In another aspect of the invention it relates to the utilization of the gaseous products or residue gas from an aromatization process. In still another its aspects the invention relates to the use of said gaseous products or residue gas with little or no purification for the alkylation of hydrocarbons. In still a further aspect the invention relates to a catalytic alkylation process in which certain gases containing the desired alkylating agent and any undesirable acetylene resulting from a hydrocarbon conversion operation are employed while avoiding catalyst deterioration which ordinarily would be caused by the use of the said gases without a prior purification. In still another aspect the invention makes economically feasible the use of a process for the preparation of benzene, and other aromatics, by cracking hydrocarbons at elevated temperatures for extended periods of time, by virtue of its particular alkylation process aspect. The preparation of benzene and aromatics by cracking having been thus rendered economically feasible, the advantages of the combination process are further increased by virtue of its pebble heater aspect, all as will appear from a consideration of that which follows.

It is well known that benzene and other aromatics are formed when hydrocarbons are cracked at elevated temperatures for extended periods of time. In the past this process has not been found profitable because the yield of aromatics is not great enough to support the operation alone, and no ready sale other than as fuel existed for the gaseous products produced.

We have discovered that the gaseous products produced when hydrocarbons are cracked to aromatics, especially as in the pebble heater operation, for example, at temperatures in the range 1300-1900 F., preferably 1475-1675 H, which is set forth and described herein, are well-adapted to the production of diisopropyl with little or no purification. These gases comprise hydrogen, methane and ethylene, with minor amounts of acetylene, propylene and higher-boiling hydrocarbons. Patent No. 2,534,089, issued December 12, 1950, discloses and claims a pebble heater. Other patents directed to pebble heaters are also extant.

When reacted with isobutane in the presence of an AlCls catalyst ethylene is converted into diisopropyl with an efiiciency as high as 85 percent. Propylene is also alkylated, but the alkylate produced is of considerably poorer quality than the ethylene alkylate. The said minor amount or low propylene content of the gaseous products, made and/or used according to this invention, therefore results in an exceptionally high-quality alkylate without the need for separating propylene.

As stated the gaseous products, or residue gas, from the production of aromatics can be used in an alkylation step with little or no purification. It is usually desir- "ice able, however, to free the residue gas of C4 and heavier hydrocarbons.

It should also be noted that in the alkylation of isoparaflins with light olefins, in the presence of aluminum chloride-hydrocarbon complex catalyst, the acetylene or like relatively very active materials such as butadiene and the like, even when present in a certain minimum amount, have such a pronounced and deleterious effect on the catalyst that its activity to maintain olefin conversion is decreased. Thus, it has been found that each pound of acetylene entering a reactor in which a mixed ethylene-propylene feed is being alkylated with isobutane will render inactive approximately 4 pounds of aluminum chloride for the production of diisopropyl. Propylene also appears to have a similar but less pronounced effect. The presence of butenes is also deleterious. In the case of excess propylene or butene not only is aluminum chloride consumption increased but the catalyst may become sufficiently viscous to render the process inoperative.

The relatively very active materials to which reference has been made are acetylene, butadiene, butenes and the like. Other such materials may be present as indicated. For example, a gas stream resulting from the cracking of a light hydrocarbon gas, or from the severe cracking of a hydrocarbon oil, will be a cracked gas containing ethane, propane or normal butane along with acetylene, methylacetylene, allen (propadiene) and the like. Some of the gases which are undesirable in the sense that they cause deterioration of the catalyst will do so even though present in rather minor quantities. It should be considered that the constant addition to the catalyst of even a very small percentage of such gases results, over a period of time, in an accumulation of undesirable material upon, in or in combination with the catalyst.

According to the invention described and claimed in copending application, Serial No. 278,566, filed March 26, 1952, by the instant inventors, it has been found that the presence of a certain proportion of hydrogen in the feed gases to the alkylation step serves to prevent otherwise undesirable deterioration or other adverse effect upon the catalyst which is due to the acetylene or other reactive hydrocarbons and therefore the hydrogen in the gases is retained and fed therewith to the alkylation zone. In the event that insufficient hydrogen is present in said gas for the purpose of the said invention, additional hydrogen can be added to the gases.

In view of the invention of the above-mentioned application for patent, it has now been found further that the gases resulting from an aromatization process according to the present invention are usable in an ensuing alkylation operation, which renders the aromatization, as herein described and claimed, economically feasible.

According to the present invention there is provided an improved pebble heater and treater combination for the cracking of hydrocarbons to produce aromatics. Also, according to the invention, the gases thus produced can be used in an alkylation step as and in the manner described and claimed herein. Therefore, as a further feature of the present invention there is provided an improved combination of a pebble heater and treater in combination with an improved alkylation operation Which is provided directly with the gases resulting from said cracking.

Referring now to the drawing, which shows diagrammatically in modified form a pebble heater and treater combination, of the invention, in combination with an alkylation operation according to the invention, the stock to be cracked to produce aromatics is fed through conduit 2 into a preheated pebble heater 3 in which it is heated to a desired temperature, for example, in the neighborhood of 1500" F. and then is passed through conduit 4 into soaker 5 wherein aromatization is completed, following which the cracked stock vapors are passed through conduit 6 into pebble p-reheater 7 wherein simultaneously there are etfected preheating of pebbles therein and passing therethrough as well as a preliminary cooling of the cracked and aromatized vapors, the pebbles also serving as a filter to at least partly remove coke and tar which, as will be seen, are subsequently burned, thus providing some heat for the process. The vapors are remo ed from pebble preheater 7 through conduit 8 and passed to tower 9, to which reference will be made hereinafter. Preheated pebbles coated with some coke and tar are passed from pebble preheater 7 through conduit 10 into pebble heater 11 wherein the pebbles are simultaneously heated for use in heater 3 and denuded of whatever coke and tar accumulation they possess. The heated pebbles are then passed through conduit 12 into the pebble cracking heater 3. Pebbles which have given up heat in heater 3 are circulated in known manner from heater 3 by means of diagrammatically illustrated apparatus 14, l5, l6, and 17 to pebble preheater 7 and pebble heater 1] respectively. The diagrammatically illustrated apparatus can be a bucket elevator. gas lift or other equivalent means.

Returning to tower 9, there is provided an oil quench 4.9 in the tower to maintain the tower bottom at about 00 F. or other suitable temperature to separate tar which is removed through conduit 13. Overhead from tower 9 passes through conduit 18 into tower 19 wherein there is employed a quench 20 which can be similar to that employed in tower 9. The temperature at the bottom of tower 19 is maintained at about 100" F. or some other suitable temperature so that lighter products will be removed or taken oil? as overhead from tower 19 and passed through conduit 21 to scrubber system 22, in which light liquid products are removed from the gases. Liquid products are drawn otf through conduit 23 and the gases are passed through conduit 24 to alkylation reactor 25 in which said gases are contacted with a preponde-rant proportion of isobutane either added to the system through conduit 26 and/or recycled to reactor 25 through conduit 27. 26. and 24. Efiluent from reactor 25 is passed through conduit 28 to settler 29 in which a gas phase. a hydrocarbon phase and a catalyst phase are formed. The gas phase is withdrawn through line 50 and passed to a vapor recovery system not shown. A portion of this gas may be recvcled to reactor 25 is desired, though this is usually not done. Catalyst is withdrawn from settler 29 through conduit 30 and is recycled through conduit 31 and 32 to reactor 25. Continuously or intermittently some of the catal st coming from settler 29 can be withdrawn through conduit 33 for refortification or discard as desired. Also fresh catalyst. or ingredients thereof. can be added to the system through conduit 34. The hydrocarbon phase formed in settler 29 is withdrawn therefrom through conduit 35. A portion of the hydrocarbon eflluent is recycled throu h conduit 36. and cooling means not shown, to conduit 26 and by way of conduit 24 to reactor 25 to control the temperature therein. The remainder of the effluent from settler 29 is passed into a caustic treater 37 from which it is passed through conduit 38 to fractionator 39 from which Ca and lighter gases are taken off as overhead through conduit 40. The bottoms from fractionator 39 are withdrawn through conduit 41 and passed to fractionator 42 in which isobutane is separated from alkylate product and returned to the process through conduit 27 while alkylate product is removed through conduit 43.

The material for quenches 49 and 20 can be supplied from any suitable source but preferably is supplied employing the bottoms from tower 19, the said bottoms being withdrawn therefrom through conduit 45 and being passed by means of pump 46 and cooler 47 to quenches 49 and 20. Any excess quench stock can be withdrawn through conduit 48. The excess quench liquid carried in line 48 may be combined with the liquid products from line 23 and passed to a purification zone, not shown. From this stream, the aromatic products, benzene, toluene, xylene, etc., will be obtained, as well as cyclopentadiene and butadiene.

The catalysts which can be employed in the process of the invention are well-known in the art. Thus in the reactor 25 there is maintained an aluminum halide-hydrocarbon complex catalyst activated as known in the art with a hydrogen halide. The catalyst usually is made up using aluminum chloride. As indicated above, fresh catalyst can be added periodically or continuously to the mass of catalyst in circulation in the process and a portion of the mass can be withdrawn therefrom in order to maintain a constant desired activity of catalyst. The hydrogen halide usually will be hydrogen chloride, either added as such, or produced in situ, using a corresponding quantity of water or in other suitable manner.

To more fully describe the invention, a hydrocarbon gas comprising ethane, propane, or butane is cracked in a pebble heater having 6 I. D. x 7 pebble heating zone in which pebbles are heated by countercurrent contact with hot combustion gases, whose temperature ranges from about 1450 F. upwards, preferably 1800 F. to about 2600 F., depending upon the other conditions. The cracking zone in which the feed gas is contacted countercurrently with hot pebbles from the heating zone is 4 /2 I. D. x 6'. Preheated steam may be used in the dome of the cracking chamber to minimize carbon formation if desired. Conditions of temperature throughput and pebble flow are adjusted so that the olefin content of the cracked gas entering soaking chamber 5 is maximum or slightly below, as shown in Table I under Cracked Gas Composition" for n-butane, propane and an ethanepropane mixture. The soaking chamber is a 7 x 10' insulated vessel and operates at approximately 1550" F. and 3.8 p. s. i. g. pressure. Residence time is approximately 3.9 seconds. The hot gas is cooled to 900 to 1000 F. by countercurrent contact with moving pebbles in chamber 7 and further quenched in 9 and 19 as previously mentioned. Aromatic tar, substantially free of toluene and lower-boiling aromatics, is withdrawn at 13.

The residue gas, free of C4 and heaviers, but containing acetylene and other reactive hydrocarbons, is compressed to 420 p. s. i. g. and charged to the reactor which is equipped with an eflicient stirrer. Isobutane in the amount of 4 mols per mol of olefin, recirculated hydrocarbon in amount to control temperature rise across the reactor to about 5 F. and catalyst amounting to about /i the volume of the total hydrocarbon feed are also charged to the reactor. Reaction temperature is 110 F., pressure 400 and time 20 minutes. Hydrogen is present during the reaction.

In soaking drum 5, sufficient time is provided to permit the aromaticas-forming step to be eflected. The reaction time required varies with temperature. Temperatures may range upwards from about 1250 F., preferably upwards of about 1300 F. Short reaction times result in liquid products containing up to 50 percent of olefins and diolefins, including cyclopentadiene, relatively small tar yields, and in addition relatively large amounts of ethylene in the gaseous products. Very long reaction times result in low unsaturation in the volatile aromatic oils, which may reach 90 percent benzene and 7 percent toluene, high yields of tar and carbon, and relatively small yields of ethylene. Normally we prefer to operate the aromaticsforming step at intermediate conditions of time-temperature, and at pressures below about 50 p. s. i. g. Under these conditions, an aromatic light oil containing about percent benzene is produced, tar production is reduced and high ethylene yields are obtained. The relation between time and temperature to produce the desired degree of cracking is given by the following equation:

5 Where I is time in seconds-andT is reaction temperature in F.

Table I records data exemplifying theoperation of the overall combination of the invention.

Table l Orackin Ste Feet? Sto k n-Butane Propane 1 02-0;

.Mixture Feed to cracking zone, lb./day 120, 000 118,000 319, 000 Pebble circulation, lb./hr 85, 000 35, 000 35, 000 Vol. iuel gas (1,000 B. t. u./c. f.),

c. i./hr 16, 000 16,000 16, 000 Combustion temperature, F 2, 400 2, 400 2, 400 Vol. preheated steam to cracking chamber dome, lb./hr 2, 400 2, 400 2, 400

Cracked Gas Composition, M01 percent 10. 6 17. 6 21. 7 33. 3 29.0 25. 1. 0 l. 0 0. 9 27. 2 27. 3 23. 7 5.0 3. 1 15. 2 12. 9. 6 2. 3 0.7 9. 4 5. 0 2. 7 L3 0, 7 4. 0 0. 4 l 3.0 1. 3 0. 5

Soaking time, sec 3. 9 3. 6 3.1 Benzol Cut: Vol., gaL/day. 2, 700 2, 500 2, 050 Approximate Composition, W percent:

C, and lighter- 6. 2 Ce unsaturate. 1.0 Benzene r 82. 8 C unsaturute. .1 0. 5 Toluene 9. 5 Aromatic tar, gaL/day 1,050 1, 530 Alkylation Step:

Olefin Feed (Residue Gas from Cracking Step)- Volume, MCF/day 1, 800 2, 060 2, 600 Total olefin, lb 31, 000 29, 700 31, 500

Composition, mol percent:

H 17. 1 23. 4 3D. 5 59. 1 57.1 53. 2 0. 8 D. 6 0. 4 20. 6 16. 9 l4. 3 2. 4 2. 0 1. 6

Isobutane (galJday):

Fresh feed 12, 900 12, 200 13, 700 Recycle 38, 000 35, 800 38, 500 Hydrocarbon recirculation (gakl day) 470, 000 450, 000 500, 000 Catalyst circulation (gaL/(lay 273, 000 262, 000 280, 900 AlCL-i (lb/day) 750 715 190 Reaction Conditions:

Reaction temp, F 110 110 110 Reaction pressure, p. s. l. g"... 400 400 400 Alkylate (gaL/day) 13, 500 12, 900 14,200

I 5% methane, 20% ethane, 74% propane and 1% butane.

An incidental but nevertheless extremely important advantage of the invention resides in the elimination of expensive equipment for separating hydrogen, methane, etc. The cost of gas compression is relatively low and the requirement for gas compression in the process is low. Hydrogen is thus introduced into the alkylation reactor, and has the desirable effect of increasing catalyst life by minimizing adverse effects of reactive hydrocarbons, particularly of acetylencs, butadiene and the like. This efiect makes possible still further simplification of the gas purification system, since removal of acetylene and the last traces of butadiene is unnecessary. The net result, therefore, is a considerable simplification of the process, coupled with increased cfiiciency and enhanced catalyst life.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention, the essence of which is that a novel and considerably improved pebble heater and treater combination for the cracking of hydrocarbons to produce aromatics and other valuable products has been provided and that gases resulting from the said cracking of hydrocarbons to form aromatic hydrocarbons are utilized in an alkylation operation as described, thereby making economically feasible the said aromatic hydrocarbon forming operation.

We claim:

1. In a pebble heater aromatization process in which a hydrocarbon material is contacted with preheated pebbles under aromatization conditions, the improvement which comprises subjecting such a hydrocarbon material to contact with preheated pebbles in a heating zone and thereby heating said material to a temperature in the range 1250 to 1900 F passing hydrocarbon cfiluent from said heating zone to a soaking zone and therein maintaining the hydrocarbon effluent out of contact with pebbles at an aromatization temperature of at least 1250 F. for a period of time sufficient to effect substantial aromatization; passing aromatized effiuent from said soaking zone to a heat-exchange zone and therein contacting said aromatized effluent with pebbles, thereby transferring heat from said aromatized effluent to said pebbles; withdrawing cooled hydrocarbon efiluent from said heat-exchange zone and recovering an aromatic-containing material as a product of the process; passing pebbles from said heat exchange zone directly to a pebble preheating zone and therein preheating said pebbles; and passing preheated pebbles to said heating zone to impart heat to said hydrocarbon feed as aforesaid.

2.. In a pebble heater aromatization process in which a hydrocarbon material is contacted with preheated pebbles under aromatization conditions, the improvement which comprises subjecting such a hydrocarbon material to contact with preheated pebbles in a heating zone and thereby heating said material to a temperature in the range 1250 to 1900" F.; passing hydrocarbon efiluent from said heating zone to a soaking zone and therein maintaining the hydrocarbon eifiuent out of contact with pebbles at an aromatization temperature of at least 1250 F. for a period of time defined by the equation T l0g1ot-(9.l 550.3) 180 wherein t is the time in seconds and T is a temperature within the aforementioned range, thus effecting aromatization; passing aromatized effluent from said soaking zone to a heat-exchange zone and therein contacting said aromatized efiluent with pebbles, thereby transferring heat from said aromatized cffiuent to said pebbles; withdrawing cooled hydrocarbon effiuent from said heat-exchange zone and recovering an aromatic-containing material as a product of the process; passing pebbles from said heat exchange zone directly to a pebble preheating zone and therein preheating said pebbles; and passing preheated pebbles to said heating zone to impart heat to said hydrocarbon feed as aforesaid.

3. An aromatization process which comprises passing a hydrocarbon selected from the group consisting of ethane, propane and butane to a heating zone and therein contacting said hydrocarbon with preheated pebbles, thus heating said hydrocarbon to a temperature in the range 1250 to 1900 F.; passing efiluent from said heating zone to a soaking zone and therein maintaining the efilucnt out of contact with pebbles at a temperature of at least 1300 F. for a time in the range defined by the equation T logiu t- (9.1103 180 wherein t is time in seconds and T is the temperature within the aforesaid range; withdrawing aromatized effluent from said soaking zone and passing said aromatized effluent to a heat-exchange zone wherein said efiiuent is contacted with pebbles and is cooled to a temperature in the range 900 to 1000 F., thereby imparting heat to said pebbles; removing thus cooled aro-matized efiiuent from said heat-exchange zone and recovering aromatic hydrocarbons therefrom as products of the process; passing heated pebbles from said heat-exchange zone directly to a pebble preheating zone and therein preheating said pebbles with hot combustion gas at a temperature in the range 1800 to 2600 F.; and passing thus preheated peb- 7 bles to said heating zone to heat hydrocarbon as hereinbefore described.

4. A process according to claim 3 wherein pebbles from said heating zone are passed to said pebble preheating zone and at least part of said pebbles are passed through said heat exchange zone prior to being passed to said pebble preheating zone.

5. A process, for the simultaneous production of aromatic and isoparafiinic hydrocarbons, which process comprises heating a hydrocarbon having from 2 to 4 carbon atoms per molecule, in a heating zone, by contact with preheated pebbles, to a temperature in the range 1250 to 1900 F.; removing hydrocarbon eifiuent from said heating zone and passing said effluent to a soaking zone; maintaining said effluent in said soaking zone, out of contact with pebbles, at a temperature of at least 1300 F. for a time in the range defined by the equation 1ogmt=(9.1i 0.3) go wherein t is time in seconds and T is a temperature in the aforementioned range; withdrawing an aromatized effiuent from said soaking zone and passing said aromatized effluent to a heat exchange zone; contacting said aromatized effluent with pebbles in said heat exchange zone and thereby cooling said aromatized effluent and imparting exothermic heat of aromatization to said pebbles; passing thus heated pebbles directly to a pebble preheating zone and therein further heating said pebbles; passing thus preheated pebbles to said heating zone to heat hydrocarbon as previously described herein; passing pebbles from said heating zone to said heat exchange zone and to said pebble preheating zone; recovering an aromatic hydrocarbon-containing fraction from the cooled efiluent from said heat-exchange zone; removing hydrocarbons having at least 4 carbon atoms per molecule from the resulting hydrocarbon effiuent from which aromatic hydrocarbons have been removed; and recovering a remaining fraction which comprises ethylene, hydrogen and small amounts of acetylene and which is suitable as a feed for alkylating isobutane with ethylene in the presence of an aluminum halide alkylation catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,196,831 Hull et a1 Apr. 9, 1940 2,233,363 Frey et a1 Feb. 25, 1941 2,296,511 Frey et a1 Sept. 22, 1942 2,298,383 Ipatiefi' et a1 Oct. 13, 1942 2,381,168 Hufi Aug. 7, 1945 2,396,697 Gorin Mar. 19, 1946 2,437,383 Dalton Mar. 9, 1948 2,439,730 Happel Apr. 13, 1948 2,459,636 Penney Jan. 18, 1949 2,477,502 Utterback et a1 July 26, 1949 2,499,624 Bergstrom et a1 Mar. 7, 1950 2,530,731 Robinson et a1 Nov. 21, 1950 2,534,090 Weber et al Dec. 12, 1950 2,696,511 Bailey et a1 Dec. 7, 1954 OTHER REFERENCES Reaction of Pure Hydrocarbons" (Egloff), Reinhold Publishing Corp., New York, New York, 1937 (pp. 111- 112 relied on). 

1. IN A PEBBLE HEATER AROMATIZATION PROCESS IN WHICH A HYDROCARBON MATERIAL IS CONTACTED WITH PREHEATED PEBBLES UNDER AROMATIZATION CONDITIONS, THE IMPROVEMENT WHICH COMPRISES SUBJECTING SUCH A HYDROCARBON MATERIAL TO CONTACT WITH PREHEATED PEBBLES IN A HEATING ZONE AND THEREBY HEATING SAID MATERIAL TO A TEMPERATURE IN THE RANGE 1250 TO 1900*F., PASSING HYDROCARBON EFFUENT FROMROM SAID HEATING ZONE TO A SOAKING ZONE AND THEREIN MAINTAINING THE HYDROCARBON EFFLUENT OUT OF CONTACT WITH PEBBLES AT AN AROMATIZATION TEMPERATURE OF AT LEAST 1250*F. FOR AA PERIOD OF TIME SUFFICIENT TO EFFECT SUBSTANTIAL AROMATIZATION; PASSING AROMATIZED EFFUENT FROM SAID SOAKING ZONE TO A HEAT-EXCHANGE ZONE AND THEREIN CONTACTING SAID AROMATIZED EFFLUENT WITH PEBBLES, THEREBY TRANSFERRING HEAT FROM SAID AROMATIZED EFFLUENT TO SAID PEBBLES; WITHDRAWING COOLED HYDROCARBON EFFLUENT FROM SAID HEAT-EXCHANGE ZONE AND RECOVERING AN AROMATIC-CONTAINING MATERIAL AS A PRODUCT OF THE PROCESS; PASSING PEBBLES FROM SAID HEAT EXCHANGE ZONE DIRECTLY TO A PEBBLE PREHEATING ZONE AND THEREIN PREHEATING SAID PEBBLES; AND PASSING PREHEATED PEBBLES TO SAID HEATING ZONE TO IMPART HEAT TO SAID HYDROCARBON FEED AS AFORESAID. 